Hi Voicy, at little tip for you re the noisy tensioner.
I did this tip on my vehicle last December is it's still as quiet as the proverbial.
"The Penny trick": takes about 5 mins to do and usually quietens most Tdi 300 squeals:
1. Tension the idler so you can remove the belt, then release tension;
2. Slacken the fixing bolt that holds the idler assembly to the engine block
then slide a penny between the block and the assembly at the 9 'o clock position (not at 9 'o clock at night, as one wag suggested !!) and retighten the fixing bolt;
3.Re assemble the belt and fire her up, hopefully the noise will be gone
Cheers & good luck, any questions just pm me,
Dave